The present invention relates to a working apparatus, especially a motor-driven tool, and to a method for operating a working apparatus of this general type. In general, the working apparatus has an internal combustion engine which drives at least one tool via a clutch, wherein the clutch initiates the clutch engagement process at a lower or initial engagement speed when the internal combustion engine is accelerated. The usual internal combustion engine has a piston, an ignition device and an ignition control device for controlling the ignition timing, such that a first ignition timing is provided for idling and a second ignition timing is provided for full load operation, wherein the second ignition timing is “earlier” than (advanced with respect to) the first ignition timing.
Machines having a tool which is driven by an internal combustion engine are well known. For example, DE 38 17 471 C1 describes an ignition system for the internal combustion engine in a working apparatus of this kind. The ignition system is provided with different characteristic curves for determining the ignition timing to be used for low speeds below the idling speed, specifically depending on whether the internal combustion engine has just been started (cold) or is in normal operation (warm).
If the supply of combustion air and fuel is heavily throttled in an internal combustion engine operating at full load, for example, because a throttle flap is suddenly closed, the speed drops. Depending on the design of the engine, the drop in speed can take place in rich mode (rich come down) or in lean mode (lean come down).
If biofuel varieties which have a high alcohol content are used, the behavior of an internal combustion engine during the drop in speed can change. Thus, an internal combustion engine which decelerates in rich mode when using conventional fuel can decelerate in lean mode with biofuel. In the event of a lean drop in speed, the internal combustion engine can remain for an undesired long time at a high speed level. This is perceived audibly by the operator and is undesirable.